~St. Gregory Palamas
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"Suppose...that a person has purified his intellectual energy through diligence in prayer, and has been to a certain extent enlightened either by the light of knowledge or in addition by noetic illumination: if he considers himself for this reason to be pure he deceives himself and is utterly mistaken, and through his presumption he throws wide open a door into himself for the devil, who always strives to delude us human beings. But if he recognizes his heart's impurity, and is not filled with pride because of the partial degree of purity he has attained, but uses it as an aid, then he will see more clearly the impurity of the other powers of his soul and will progress in humility; his inward grief will grow and he will find suitable ways of healing each of his soul's powers. He will cleanse its moral aspect with the right kind of ascetic practice, its power of spiritual apperception with spiritual knowledge, its power of contemplation with prayer; and in this way he will attain perfect, true and enduring purity of heart and intellect - a purity that no one can ever experience except through perfection in the ascetic life, persistent practice, contemplation and contemplative prayer."
+ + +" 'Be attentive to yourself,' says Moses (Deut. 15:9.LXX) - that is, to the whole of yourself, not to a few things that pertain to you, neglecting the rest. By what means? With the intellect assuredly, for nothing else can pay attention to the whole of yourself. Set this guard, therefore, over your soul and body, for thereby you will readily free yourself from the evil passions of body and soul. Take yourself in hand, then, be attentive to yourself, scrutinize yourself; or, rather, guard, watch over and test yourself, for in this manner you will subdue your rebellious unregenerate self to the Spirit and there will never again be 'some secret iniquity in your heart' (Deut. 15:9)."